Sheets of randomly distributed continuous filaments



- 1 3,341,394 SHEETS OF RANDOMLY DISTRIBUTED CONTINUOUS FILAMENTS FiledDec. 21, 1966 G. A. KINNEY Sept. 12, 1967 '7 Sheets-Sheet l FIG.

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vINVENTOR GEORGE ALLISON KINNEY BY ATTORNEY Sept-12, 1967 *G. A KINNEY3,341,394

SHEETS OF RANDOMLY DISTRIBUTED CONTINUOUS FILAMENTS Filed Dec. 21, 1966'7 Sheets-Sheet 2 FIG.5

FIG.4

INVENTOR AVJJ GEORGE ALLISON Kl EY ATTORNEY G. A. KINNEY Sept. 12, 1967SHEETS OF RANDOMLY DISTRIBUTED CONTINUOUS FILAMENTS 21, 1966 7Sheets-Shet 3 Filed Dec.

INVENTOR GECIRGE ALLISON KINN Y. BY M ATTORNEY G. A. KINNEY Sept. 12,1967 Filed Dec.

7 Sheets-Sheet 4 VI ma N EN V M N O S L L A E G R O E G ATTORNEY G. A.KINNEY Sept. 12, 1967 SHEETS OF RANDOMLY DISTRIBUTED CONTINUOUSFILAMENTS 21, 1966 7 Sheets-Sheet '5 Filed Dec.

Fl 6. I'OA FIG. IOB

DISTANCE ALONG WEB (IN) INVENTOR GEORGE ALLISON KINNEY ATTORNEY I00 H0I20 CV 0F FILAHENT SEPARATION G. A. KINNEY Sept. 12,1967

SHEETS OF RANDOMLY DISTRIBUTED CONTINUOUS FILAMENTS Filed Dec. 21, 19667 Sheets-Sheet 6 FIG. IIB

FIG. IIA

FIG. IID

FIG. IIC

INVENTOR GEORGE ALLISON KINNEY Y A m w A Sept. 12, 1967 G. A. KINNEY3,341,394

SHEETS OF RANDOMLY DISTRIBUTED CONTINUOUS FILAMENTS Filed Dec. 21, 19667 Sheets-$heet 7 FIG.I3

naazavehia tjmwaw INVENTORQ GEORGE ALLISON KINNEY ATTORNEY United StatesPatent ()fifice 3,341,394 Patented Sept. 12, 1967 3,341,394 SHEETS FRANDOMLY DISTRIBUTED CUNTHNUOUS FILAMENTS George Allison Kinney, WestChester, Pa., assignor to E. 1. du Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware Filed Dec. 21, 1966, Ser.No. 613,370 11 Claims. (Cl. 16172) This application is acontinuation-in-part of copending application Ser. No. 439,361, filedMar. 12, 1965, which in turn is a continuation-impart of applicationSer. No. 133,736, filed Aug. 24, 1961, and now abandoned, which in turnis a continuation-in-part of application 'Ser. No. 859,614, filed Dec.15, 1959, and now abandoned, and is also a continuation-in-part ofcopending application Ser. No. 515,308, filed Dec. 21, 1965, which inturn is a continuation-in-part of application Ser. No. 345,792, filedFeb. 18, 1964, which in turn is a continuation-in-part of applicationSer. No. 200,257, filed June 5, 1962, and now abandoned, which in turnis a continuation-in-part of application Ser. No. 859,661 and Ser. No.859,614, both filed Dec. 15, 1959, and now abandoned.

This invention relates to nonwoven Webs, fabrics and related sheetstructures based on continuou filament synthetic organic fibers.

Continuous filament batts of glass fibers are known and are commerciallyavailable. The glass fibers are extruded from a melt and laid down in arandom mass. The products are especially useful as insulating materials.In some cases, such glass fiber batts are used as reinforcing elementsin plastic articles Where the fibers provide strength and rigidity.During laydown of the batts, filament aggregation occurs and ropystrands of a plurality of filaments are present in the nonwoven sheetproduct. Since the continuous filament fibers are usually only a smallportion of the final product, the appearance of the fibers and theparticular manner of distribution had. not been considered important.However, it is the aforementioned structural characteristic of the priorart sheets even apart from the materials employed that is responsiblefor most of their deficiencies for a variety of applications. Syntheticorganic polymer materials are sometimes suggested in patent literatureas equivalents for the glass fibers in such batts.

Nonwoven sheet structures derived from staple fiber materials havebecome increasingly popular for apparel and commercial uses. At the sametime, such uses have brought awareness of the deficiencies of theproducts, in particular their lack of high tensile strength andresistance to tear. It is well-known that felts and papers are ingeneral lacking in these properties. Many ingenious developments havebeen devised, chiefly, involving preferred binder materials, with thestaple fiber sheet products of higher tensile and tear strength. It hasnot hitherto been recognized that high quality sheet structures ofcontinuous filament synthetic organic fibers could be prepared so as togive uniform, strong sheet structures of the type desired in manyapplications now served by woven fabrics. Commercial operations havebeen restricted in that, except in certain limited applications such asinsulating batts, and high tenacity binding tapes, use of continuousfilament organic fibers has not been feasible.

Fiber processing techniques which are known in the art will not providea sheet which is uniform in fiber distribution when continuous filamentsynthetic organic fibers are employed. Indeed this is no simple problem.Continuous filament synthetic organic fibers are normally prepared athigh speeds. They are prepared in large bundles of 30, 50 or evenseveral hundred individual fiber elements all emerging simultaneouslyfrom a multi-holed spinneret.

goal of producing nonwoven Deposition of a filament bundle from such aspinneret in the form of a web inevitably leads to ropy sheet structurescomposed of overlapping bundles of parallel filaments.

It is an object of the present invention to provide superior continuousfilament synthetic organic fiber materials in the form of nonwoven sheetstructures to permit greater utilization of the inherent high strengthof modern synthetic fiber materials without the necessity of expensiveand laborious weaving operations. It is a further object to providesubstantially isotropic nonwoven sheet structures of uniform appearanceand having superior tensile and tear strength which comprise continuousfilament synthetic organic fibers distributed in the sheet in ahomogeneous random manner.

Another object is to provide coherent nonwoven continuous filament webswhich, even without bonding, are strong enough to permit continuoushigh-speed processing in such operations as dipping, impregnating,mechanical deforming, laminating and other commercial treatment, withoutrequiring support of special handling of the web.

These objects have now been achieved in nonwoven sheet structures ofcontinuous filament organic fibers in which the individual filamentmembers are disposed in random configuration uniformly throughout thestructure and in which the individual filamentary members are sodisposed as to be separate, independent, and nonparallel in theirrelationship to one another. It is only through the utilization ofcontinuous filament nonwoven structures that it is possible to achieveeven to an approximate level the full utilization of the inherenttensile strength of the present day synthetic organic filaments incombination with high tear strength and flexibility in the nonwovenstructure. This unusual combination of properties is obtainable withcontinuous filament structures because they do not require a high levelof binder to obtain strong fabrics, thus tear resistance and flexibilitycan be maintained. With staple fiber structures, a higher level ofbinder is required to obtain strong fabrics and this is detrimental toboth tear resistance and flexibility.

The sheet structures of this invention are composed of randomlydistributed continuous synthetic organic filaments, preferably of adenier in the range of 0.1 to 30 (0.01 to 3.3 tex.). The individualfilaments are separate and independent of each other as defined by acoefiicient of variation of filament separation, as hereinafterdescribed, of less than 100%. The filament separation can also becharacterized by a bunching coefficient, as hereinafter, described, of0.7 or greater. Depending on the method of preparation, the individualfilaments also may exhibit quite high levels of crimp. Such crimpedfilaments are highly desirable as components of the nonwoven webs ofthis invention, and it is a surprising and advantageous feature of theseproducts that even the use of crimped filaments does not interfere withachieving the indicated high level of filament separation.

Because of the individual, random distribution of the filamentaryelements of the nonwoven webs of this invention, and the substantialabsence of filament aggregates, the sheets are uniform in appearance andin opacity to light. In general, such webs will have a high level of Webcoherence and sheet strength, i.e., above 0.3 lb./in./oz./ yd. beforebonding. Such high strength permits the webs even Without bonding to bereadily handled at high speeds for any necessary or desired processing.In order to obtain such nonwoven sheet structures it is necessary thatindii bunching is by means of the distribution of the filamentseparation distances. The coefficient of variation of the filamentseparation distances, hereinafter referred to as CJf is used todescribed this distribution because it provides a normalization so thatwebs of different density can be compared.

A web which is formed from bundles of filaments in which there has beenno attempt to separate the filaments within the bundles will containbunches of filaments and the CV will be much greater than 100%. Such aweb will vary widely in density and appear blotchy. Similarly, webscontaining numerous filament entanglements present CV valuessubstantially above 100%. On the other hand, if special care is taken toprovide for uniform filament separation prior to and during formation ofnonwoven webs from continuous filaments, webs with a CV of less than100% can be obtained. A surprising finding is that the nonwoven webs ofthis invention, which have a CV of 100 or less are markedly dififerentfrom webs having a CV greater than 100%. A nonwoven web of thisinvention, when compared with a nonwoven web of the same type ofcontinuous filaments but having a coefficient of variation greater than100%, will (1) have much greater strength at equal filament tenacity,(2) have significantly better :and more uniform appearance, (3) havegreater abrasion resistance, and (4) have improved degree ofwaterproofness at a given weight of coating.

The bunching coefficient can also be used to describe the degree offilament aggregation. Bunching coefficient, designated BC, is defined asthe ratio of the fiber spaces occupied by fibers relative to the totalnumber of fiber spaces available. In this measurement the term fiberspace represents the average space occupied by a fiber, and iscalculated by dividing a unit distance of the non woven sheet structureby the total number of fibers oriented in a single direction in thatunit length. The bunching coefficient concept is based on the premisethat where the individual fibers disposed in the same direction areuniformly spaced from each other, each fiber space will contain onefiber and the bunching coefficient of such a structure will be unity. Ina nonwoven which contains bunched fibers, some of the fiber spaces willcontain bundles of fibers while others will be unoccupied and thebunching coefiicient of such a structure will be less than one. Bunchingcoefiicient, however, is insensitive to the location of the filamentswithin the fiber space, so that an accurate measure of the structuralcharacteristics of the web is not always obtained. Since thedistribution of distances between essentially parallel fialment segmentsdoes directly described the structure, CV is the preferred measure offilament separation.

A further characteristic which is essential to the structures of theinvention is the random disposition of the component filaments. Byrandom is implied the substantial absence of any anisotropy in thearrangement of the individual filaments. One test for randomnessinvolves cutting representative square samples one inch or greater fromthe sheet under consideration and then counting the number of filamentsterminating at each side of the square. In a random sheet of uniformbasis weight, the number of filaments that will be encountered along anyside of the square will vary by less than 20% from the number offilaments terminating at any other side of the square, regardless of thelocation or orientation of the square within the plane of the sheet. Inpreferred sheets, substantially the same number of filaments areencountered at each side of the square. A more precise and preferredprocedure for measuring randomness than that described above determinesthe actual orientation or direction in which the component filaments liewithin the plane of the nonwoven sheet. For a random sheet, there willbe no predominant orientation of the filaments within the sheet, orexpressed alternatively, there will be, on the average, as manyfilaments lying in one direction as in any other direction. This permitsmaximum utilization of the component filaments and leads to a sheetwhich has essentially equivalent properties in all directions in theplane of the sheet.

The aforementioned sheets are useful in many ways. In general, they aremost desirable and most widely used in the form of bonded sheets; thatis, fibrous webs in which the continuous filament fiber elements areinterconnected to one another with strong physical or chemical bonds.Such bonds may derive from the fiber elements themselves or from someadded binder material, of from some second structure or structuralelements which are combined with the nonwoven sheet material alreadydescribed. All of these difierent embodiments are aspects of the presentinvention.

The examples which are given below illustrate the production of unbondedwebs as well as some of the many modifications of binder technologywhich may be employed in utilization of the principles of thisinvention. Bonding procedures which may be employed are summarized hereto illustrate the wide range of useful techniques. One desirableembodiment involves nonwoven structures which have been prepared in aform providing co-spun binder fibers. Such binder fibers may consist ofcontinuous filament of a similar chemical nature to the structuralfilament element but having a lower melting point. In one mode ofoperation, such binder filaments may be filaments of the same chemicalcomposition but spun with a lower level of orientation or with noorientation. In a second mode of operation, the co-spun binder filamentsmay be highly oriented but may be of a copolymeric nature or of someother modification which provides a lower melting temperature. Preferredbinder fibers for use with poly(hexamethylene adipamide) includepolycaproamide filaments or copolymers, melt blends, etc., thereof withpoly(hexamethylene adipamide). Preferred binder fibers for use withpoly(ethylene terephthalate) include the isophthalate andhexahydro-terephthalate copolymers thereof.

Still another technique is the use of composite filaments as describedin Breen, US. Patent 2,931,091. The composite filaments may comprise ahigh-melting structural polymer and a low-melting binder polymer inside-by-side relationship running the length of the filament.

Indeed it is not necessary that any different filaments be employedsince the principle of self-bonding may be used, in which the bonds areprovided by localized fusion, partial or complete, of individualportions of the fibers. Such fusion may be brought about by sparkdischarge through the web or the application of heat to highlylocalized, mechanically isolated portions of the web. Solvent bondingmay be employed, using spray techniques or a solution dipping process.The solvent need not be a complete solvent for the polymer but aswelling agent or a wetting agent. It is also possible and within thescope of the present invention to comprehend webs which have been bondedby the application of a vaporous or gaseous material which is not itselfchemically reactive with the polymeric compositions of the filaments butwhich bonds by virture of having excess heat content' Thus, steam orhigh temperature air or other vaporous material may be used to implementbonding. Finally, the webs may be rendered more coherent merely bypressing them as freshly prepared. This self-binding technique issurprisingly satisfactory and is sufficient to produce a structureuseful for numerous applications as such. It is noted in thisself-binding procedure that the inherent settability and crimp in thecomponent filaments is believed to be in part responsible for theefficacy of the over-all operation. The instant nonwoven structures mayalso be rendered more stable to delamination by needling techniques(see, for example, Lauterbach & Norton, US. Patent 2,908,064).

In further modifications, it is possible to apply or codeposit resinousthermoplastic binder particles in the form of granules, powders, orfibrids such as those dcscribed in Morgan, US. Patent 2,999,788. In morefamiliar processing it is equally suitable to employ impregnationtechniques using solutions, emulsions, dispersions or melts of resinbinders to bring about the desired bond formation. Furthermore, it iswell within the scope of this invention to apply to the unbonded websafter formation, intermediates suitable for the formation of polymericmaterials to bring about polymerization of a binder polymer within theweb, thus in a single step creating the polymeric binder and activatingit to give a strong, bonded, highly coherent fabric. It is in the formof bonded fabrics that the nonwoven sheet structures of this inventionare most desirable.

Bonding may be applied uniformly over the entire area of the fabric orin closely controlled patterned areas or in random patterned areas. Twoor more different bonding techniques may be employed simultaneously orin sequence. In addition to bonding in itself, application of othermaterials to the nonwoven sheet structures of this invention may beemployed for other purposes such as surfacing, modification of visualappearance or opacity or porosity or for providing other physical orchemical properties of a specific desired nature.

It is also possible to laminate the nonwoven structures of the presentinvention to films or fabrics which are in themselves thermoplastic ormay contain thermoplastic elements which can be bonded to the presentwebs by the application of continuous or localized areas of heat. Withinthe scope of this aspect of the invention is included the lamination ofthe nonwoven sheet structures of this invention to metallic foils, andto impervious or pervious films. Such materials are useful for thepreparation of protective coverings, vapor seals, conductive materials,dielectrics and other articles of commerce In all of the sheetstructures described herein, it is the critical feature already setforth, that is, the high degree of randomness and uniformity of fiberseparation Within the web which is the outstanding characteristic ofthese sheet products and which makes them unique and valuable.

A method by which it is possible to process continuously a bundle ofparallel, synthetic organic fibers into a nonwoven sheet structure ofthe type described in the present invention, has been set forth inapplicants copending application Ser. No. 515,308 filed Dec. 21, 1965.That application describes a process in which a running multi-filamentbundle composed of continuous synthetic organic filaments is chargedelectrostatically under tension to a sufiicient level that, when thetension is released, the charge causes each filament to separate fromadjacent filaments, and thereafter the filaments are collected on areceiver to form a nonwoven sheet product.

The filaments may be charged by a corona discharge maintained in thevicinity, by triboelectric contact with a suitable guide means or byother suitable electrostatic methods. The charging is accomplished whilethe filaments are under sufiicient tension that they do not separateuntil such tension is released, i.e., after they have been urged towardthe receiver, whereupon they immediately separate and are thencollected. In one embodiment, freshly formed melt-spun synthetic organicfilaments are charged and are simultaneously oriented with a pneumaticjet, the action of which also serves to forward the charged filaments tothe receiver.

The invention will be more readily understood by referring to theattached drawings, wherein In FIGURE 1, A and B show schematicallyalternative apparatus assemblies useful in producing webs of theinvention from freshly spun and lagged yarn, respectively;

FIGURE 2 shows a modification of the FIGURE 1 apparatus;

FIGURE 3 shows in longitudinal section a pneumatic jet which may be usedin combination with the apparatus of FIGURES 1 and 2;

FIGURE 4 shows another modification of the apparatus of FIGURE 1;

FIGURE 5 shows in longitudinal section the pneumatic jet used with theapparatus of FIGURE 4;

FIGURE 6 shows a modification of the apparatus of FIGURE 1 using analternative charging means;

FIGURE 7 shows schematically further alternative apparatus assemblieswherein the filaments are drawn either mechanically with draw rolls orby a pneumatic jet and wherein the filaments are electrostaticallycharged with a corona discharge device;

FIGURE 8 shows schematically in longitudinal section, the nozzle portionof a pneumatic jet which may be used with either embodiment of theapparatus in FIG- URE 7;

FIGURE 9 shows schematically an optical apparatus suitable for thedetermination of randomness of nonwoven sheets;

FIGURES 10A and 10B are densitometer traces respectively of webs A and Emade as described below in Examples III and VII respectively; and

FIGURES 11A and 11B are enlarged photographs of webs whose traces areshown in FIG. 10A and FIG. 10B. FIGS. 11C and 11D are enlargedphotographs of Webs G and F, respectively, prepared as described belowin Examples IX and VIII respectively; and

FIGURE 12 shows graphically the relationship between the tensilestrength and the coefiicient of variation of filament separationdistances for a series of nonwoven webs having the same filamentstrength.

FIG. 13 is a schematic representation of a web of the invention 6t)containing both matrix filaments 50 and binder filaments 51.

FIG. 14 is a side view schematic representation of a web of theinvention 60 impregnated with a waterproofing composition 51.

FIG. 15 is a schematic representation of a web of the invention 60laminated to a. self-supporting film 70.

Referring to embodiment A of FIGURE 1, freshly formed filaments 1 arespun through spinneret 2 and pass freely rotatable, i.e., nonsnubbingidler roll 3, whereupon the filaments 1 are converged into yarn orbundle 4. Yarn 4 then is pulled through pneumatic jet 5, which iscontinuously supplied with air under pressure through air inlet 6,making triboelectric contact with the tapered inlet section or throat 7thereof. Optionally, the filaments 1 may pass directly to pneumatic jet5 without prior convergence to a yarn provided that they (the filaments)make sufficient triboelectric contact with throat 7 of pneumatic jet 5(i.e., provided that the spinneret 2 and pneumatic jet 5 are notdisposed in-line with respect to one another). The pneumatic jet 5 (andhence the throat 7 portion thereof) is electrically grounded throughlead 8. The charged filaments 9 issuing from pneumatic jet 5 arecollected as sheet 10 on receiver 11 which, in this embodiment, isgrounded through lead 12. The repelling effect due to the charge on thefilaments 9 exiting pneumatic jet 5 is indicated diagrammatically by thearrow 13 emanating from within the filament region.

Alternatively, as shown in embodiment B of FIGURE 1, yarn 4 may besupplied to pneumatic jet 5 from a package 14, prior to which the yarnhas been rendered receptive to charging (i.e., in a relatively anhydrouscondition free from charge-diminishing contaminants or finishes).Preferably, the yarn is taken off the side of the package to minimizetwisting of the yarn, which otherwise woulcl inhibit subsequent filamentseparation. In either embodiment (FIGURE 1; A or B), roll 3 need not befreely rotatable, rather it might be fixed to provide a degree ofsnubbing. The roll 3 also might be replaced by a bar or the like for thesame purpose.

FIGURE 2 shows a modification of the FIGURE 1 apparatus wherein the yarnis charged triboelectrically by contact with guide 15 locatedintermediate roll 3 and pneumatic jet 5 (shown fragmentarily). Guide 15is composed of a material which is capable of producing sufficientcharge on the filaments in yarn 4 to separate the filaments from eachother and maintain that separation until the strand strikes thereceiver. Guide 15 is located above jet 5 so that the as-charged yarnenters the jet axially. Guide 15 may be slowly rotated and/ or traversedto reduce surface wear; it can be a circular pin as shown or may be abar or the like. A certain degree of snubbing takes place on passingguide 15, depending on the coefficient of surface friction and the angleof wrap made by the yarn over the surface thereof. Additional snubbingwould result from fixing roll 3 or its equivalent as earlier described.

FIGURE 3 shows in longitudinal section a pneumatic jet which can be usedwith the apparatus of FIGURES 1 and 2. Jet 5 is assembled fromcomponents 5a, 5b, and 5c with cap screws (not shown). The assembled jetconsists of essentially cylindrical yarn passageway 19 (the extension 1%of which is shown fragmentarily) which is outwardly flared towardfilament inlet 16 in entrance section 5a to form a guide throat 7. Airunder pressure is supplied through inlet 6 to the plenum 18 and entersfilament passageway 19 through the annular slit 17. In the presentembodiment, the air passing through slit 17 encounters the filaments atan angle of about 15 thereto, whereby a forwarding motion is imparted tothe filaments. The composition of entrance section 5a (hence guidethroat 7) is important to over-all process results; in the presentembodiment, entrance section 5a is readily interchangeable.

In operation with any of the above-described apparatus, the yarn, i.e.,the filament bundle, is forwarded from the supply means and urged to thereceiver means by the action of the pneumatic jet. In the case offreshly spun filaments, the pneumatic jet (or equivalent forwardingmeans) is located beyond the point where the filaments are substantiallycompletely solidified or quenched, as are usually the associated guidemeans unless they are of the non-snubbing variety. These precautionsprevent sticking of the individual filaments. Simultaneously, theindividual filaments are charged to a high potential, positive ornegative, depending on the yarn and guide compositions, by virtue oftheir triboelectric contact therewith. A similar charging effect resultsfrom maintaining a corona discharge in the upstream vicinity of thepneumatic jet. Accordingly, as the filaments issue from the jet and areurged toward the receiver means, they immediately separate, owing to theforces of electrostatic repulsion. Partly due to the impetus received atthe jet and partly due to the attraction of the filaments toward thegrounded or oppositely charged receiver, they are deposited on thereceiver as a compact unitary structure, i.e., as the desired nonwovenbatt, sheet, web, or the like.

Referring to FIGURE 4-, freshly formed filaments 1 are spun throughspinneret 2, pass as shown over bar guides 20, 21 and 22 thence topneumatic jet 5 supplied with air under pressure through inlet 6.Pneumatic jet 5 embodies extended filament passageway extension 19flared outwardly at the terminus 23. The charged filaments 9, whichseparate on exiting the extension of jet 5, are collected on receiver11, an aluminum plate. The various components downstream from spinneret2 are grounded through leads 12. The guide bars 20, 21 and 22 are 1 in.x 1 in. with rounded edges and are composed of chromic oxide. Guide bar21, i.e., the functional surface thereof, is offset from the filamentline by 2.5 in. Pneumatic jet 5 is drawn in greater detail in FIGURE 5wherein the reference numerals have substantially the same significanceas those in FIGURE 3.

FIGURE 6 schematically illustrates another and highly desirableembodiment which involves the use of corona discharge as theelectrostatic charging means. Molten polymer is extruded through amulti-hole spinneret 2, in the form of fine filaments 1. The continuousfilaments pass through an electrostatic charging zone consisting of aset of corona discharge points 24 supplied with a high voltage by source25, together with a target electrode 26, which is grounded. The chargedfilaments pass through a pneumatic jet 5, supplied with air at 6, whichforwards them toward a collecting mechanism. The action of the pneumaticjet establishes positive tension on the filaments, causing them toundergo molecular orientation by drawing in the space between thespinneret and the jet. As the filaments emerge from the outlet 23 of thejet, the like electrical charges carried by the individual filamentscause them to repel one another and deposit on the collecting device inrandom, individual, nonparallel disposition. The collecting device shownconsists of an endless belt 11 running over rollers 27, and backed up bya grounded electrode 28. The deposited filaments form a web 10 whichpasses through consolidating rolls 29 and then on to optional laterprocessing steps, such as bonding, coating, laminating, embossing, etc.

Chargeable continuous synthetic organic filaments which are useful forthe purpose of this invention include those comprised of polyamides,such as poly(hexamethylene adipamide), polycaproamide and/or copolymersthereof; polyesters, such as poly(ethylene terephthalate),poly(hexahydro-p-xylylene terephthalate), and/ or copolymers thereof;polyhydrocarbons, such as polypropylene and polyethylene; polyurethanes,polycarbonates, polyacetals, polyacrylics, vinyl polymers, vinylidenepolymers, and the like. Filaments of different polymers may be chargedand laid on the receiver simultaneously. Preferred polymers are themelt-spinnable ones (see FIG. 1A) which can be processed from polymer tononwoven web in a single continuous operation. Otherwise the filamentsusually require preparation prior to charging, etc., by drying, removalof solvent, possible adjustment of finish, and the like.

Depending on the particular mode of filament prepa ration, theindividual filaments may exhibit a high level of crimp superimposed uponthe random arrangement of each filament within the sheet. The concept offilament crimp is understood in the art. In a filament crimp theamplitude of the departure from a straight line is less than 3 times theradius of curvature of the crimp, the latter being always less than 0.5inch. The presence of crimp in the filaments can contribute to theutility of the sheet. For example, finished structures based on sheetswherein the individual filaments exhibit crimp at levels in excess ofabout 30 crimps per inch are useful in apparel applications, owing totheir enhanced softness and drapability. At crimp levels in excess ofabout crimps per inch, the effect is especially pronounced. At crimplevels less than about 30 crimps per inch, the articles are stiffer,hence are best suited for the more demanding industrial applications,e.g., tarpaulins. Crimp enhances the stability of the sheets andcontributes to improved covering power.

Crimped filaments can be obtained by orienting the filaments immediatelysubsequent to the preparation thereof. Representative of such a processis the one described in Hebeler, US. Patent 2,604,689. Variations ofthis basic procedure are applicable to melt-spun filaments generally;the process is termed spin-drawing. It is especially useful withfilaments of poly(hexamethylene adipamide), polycaproamide, andpoly(ethylene terephthalate), including copolymers thereof. In the caseof most spun-drawn polyamides, the crimp develops spontaneously after afew minutes standing. The development of crimp is accelerated by heatand/ or moisture, i.e., by relaxing the filaments. In the case ofpoly(ethylene terephthalate), or the like compositions, a distinctrelaxation step is required, during which the filaments shrink, crimpdevelops and, in many instances, the property of spontaneousextensibility is achieved (see Kitson and Reese, US. Patent 2,952,879).Relaxation can be effected as a separate operation apart from sheetpreparation by heating the sheet, or during sheet formation proper byheat ing (steam, hot air, or infra-red radiation) the filaments withinor downstream from the pneumatic jet. The filaments may be collected ona hot water bath to effect relaxation simultaneous with collection. Inthe case of filaments supplied in accordance with FIGURE 1B, thefilaments may already be crimped, and so long as such crimp does notimpede filament separation, the method is a satisfactory one. Crimp canalso be obtained in filarnents by the process described in Kilian, US.Patent 3,118,012, or by the use of two-component filaments as disclosedin Breen, US. Patent 2,931,091. Crimp also is obtainable in filamentscomposed of thermoplastic polymers by the deformation thereof over asharp surface such as a blade or edge over which the filaments make anacute angular pass. The development of Crimp in such products also isenhanced by relaxing conditions. Other crimping procedures may also beemployed for other polymer compositions, such as polyhydrocarbons, e.g.,polypropylene. The presence of crimp in the filaments tends to causefilament entanglement and may require more careful control.

The sheets and webs of this invention may be made in varying densities.High-bulk, low-density webs, for example, are particularly useful formany nonapparel uses. Fabric densities below 0.1 g./cc. may be prepared,especially when highly crimped fibers are present. Higher densitymaterials, in the range 0.2 to 0.5 g./cc., are useful, whilehigh-density webs 0.5 g./cc. and higher, are also valuable.

DETERMINATION OF COEFFICIENT OF VARIA- TION OF FILAMENT SEPARATIONDISTANCES is) In order to measure the distance between filaments in anonwoven web, it is often necessary to section the structurelongitudinally. This may be done with unbonded webs by simpledelamination; however, with bonded Webs, this is not satisfactory sincethe initial structure is disturbed in the delamination procedure.Satisfactory sections can be obtained by a technique which involvesimbedding a 2 in. x 0.5 in. sample of web in a curable epoxy resincomposition. After curing overnight, the sample can be slicedlongitudinally with a microtome into sections 30 to 4-0 microns thick.This method has been found to be satisfactory for both bonded andunbonded webs. The distances between the filaments are then measuredwith a projection microscope set at 100x magnification for filamentshaving a denier of 4 or less and at 50X magnification for filamentshaving a denier greater than 4. Separation distances are measured alonga line which covers t least 2 in. of web; preferably however, at least 3in. of web are scanned in which case it is necessary to imbed twosamples of the web. The filament segments involved in the count arethose which are perpendicular within 12 to the line of count. At least200, and preferably 400 filaments are counted in order to characterize agiven sample. The precision of the coefiicient of variation which iscalculated from the filament distances is of the order of 13%.

DETERMINATION OF BUNCHING COEFFICIENT Number f fiber spaces occupied byfibers Total number of fiber spaces available 10 Where all fiberelements are completely parallel, and exactly uniformly spaced, thebunching coefficient is unity. The actual bunching coefiicient may bedetermined by taking a photograph of the web, ordinarily of a sample notgreater than 5 mils thick, and counting the number of fibers crossing agiven line segment at right angles to that line (using an angulartolerance level of not over 2 in considering or not considering eachfiber). The total number of fibers counted is equal to the total numberof fiber spaces in that line segment. The average fiber space width iscalculated by dividing the segment length by the number of fibers. Ascale is now constructed with unit distances equal to the average fiberspace width. With this scale, the number of fiber spaces occupied by atleast one fiber is determined. For accurate results, measurements aremade in several directions, and averaged.

DETERMINATION OF RANDOMNESS As indicated hereinabove, the mostpreciseand preferred test for randomness will determine the actual orientationor direction in which the component filaments lie within the plane ofthe nonwoven sheet. The method described by I. W. S. Hearle and P. J.Stevenson in the Textile Research Journal, November 1963, pp. 879-888,determines the randomness of a nonwoven sheet. This method requires thecounting and plotting of a large number of filaments in order to obtainaccurate and reproducible results and is, therefore, verytime-consuming. It is further noted that, whereas the actual visualmeasurement of filament orientation is readily applicable to nonwovensheets in which the fibers are predominately straight, it is not assatisfactory for sheets in which the fibers are curved or crimped.

Instead of counting the number of filaments oriented at the variousdirections within the nonwoven sheet, it has now been found that arandomness measurement can be obtained by determining the total lengthof the filament segments that are oriented at the various directionsthroughout the sheet. In a random sheet, the total length of filamentsegments at any one orientation is the same as at any other orientation.This measurement has the advantage that it is universally applicable tostraight, curved, or crimped fibers.

It has been found that the measurement of the length of filamentsegments at the various orientations can be made rapidly and accuratelyby an optical method. The method is based on the principle that only theincident light rays which are perpendicular to the fiber axis of a roundfiber are reflected as light rays which are perpendicular to the fiberaxis. Hence, by focusing a beam of parallel light rays on a nonwovensheet at an incident angle less than e.g., 60, the light which isemitted perpendicular to the plane of the sheet comes only fromfilaments having an orientation within the plane of the sheet which isperpendicular to the incident light rays. By collecting and measuringphotoelectrically the intensity of the light, the total length of thefilament segments perpendicular to the light rays, therefore, parallelto each other, can be determined. By rotating the sheet, the parallelfilament segments for any given direction can be measured and from thismeasurement, an analysis of the randomness can be made.

An apparatus suitable for this measurement is shown schematically inFIGURE 9 and will hereinafter be referred to as a randometer. A detaileddescription of the components, the method of operation, and the methodfor standardizing the characterizations are given below.

As shown in FIGURE 9, the apparatus has a revolving stage 46 on whichthe sample 47 to be examined is placed. Stage 46 is modified by gear 48which has half the teeth removed so that when driven by synchronousmotor 49, it rotates only Stage 46 rotates at 4 rpm, thus the time forrotation of the sample through 180 is 2 minutes. Lamp 50 is locateddirectly over the sample and in line with magnifying lens system 51.Lamp 50 is a 6-volt lamp and its intensity is controlled through 6-volttransformer 52 and variable-voltage transformer 53. The light from 50 isfocused by lens 51 onto the bottom of the sample, and when projectedthrough objective lens 54, eyepiece 55 and reflected from mirror 56,gives a shadow of the sample on ground-glass screen 57 at amagnification of 36X. Screen 57 is circular and has a diameter of 6.9inches.

A second lamp 58 is mounted in a housing with projection lens 59 tofocus the light on the sample at an angle of 60. Lamp 58 is a 25-watt,concentrated arc lamp receiving its power from power supply 61 which ismodified to eliminate the AC. ripple. The filaments or segments offilaments which are perpendicular to the light from lamp 58 reflect thelight into the magnifying lens and mirror system to screen 57 formeasurement. Optical slit 62 is located between the objective lens 54and stage 46 and serves to control the limits of the light reflectedfrom the sample. The slit is in. x in. and is mounted with its long axisparallel to an imaginary line which is perpendicular to the light fromlamp 58 and within the plane of the sample' The light from the screen isfocused by Fresnel lens 63 onto photomultiplier tube 64 RCA type 1P21)having a 2500-volt DC. power supply 65. The screen, Fresnel lens, andphotomultiplier tube are contained in a single light-tight unit, whichcan, however, be opened for visual observation of the screen. The outputfrom the photomultiplier tube is fed into a microampere recorder 66having a chart speed of 8 in./min. and a chart 9.5 in. Wide. The chartrecords the light reflected from the parallel filaments at eachdirection as the sample is rotated through 180. The sensitivity ofrecorder 66 should be adjusted so that a current of 6 microamperes gives100% pen deflection.

A two-way switch 67 is in the line from the photomultiplier tube to therecorder so that the signal can b measured on a sensitive microamperemeter 68, if desired. This meter can also be used in conjunction with a6-volt lamp of fixed intensity to measure the fiber density of thesample so that, if desirable, all samples can be compared on the samebasis.

Samples of the nonwoven sheet to be examined are preferably unbonded andshould permit clear viewing on the randometer of all the filamentsthrough the thickness of the samples. A preferred basis weight range forsheets of 3 denier filaments is 0.75-l.5 oz./yd. Samples in excess of1.5 oz./yd. should be delaminated to fall within the range stated, butcare should be exercised to avoid the introduction of directionality dueto the delamination. The delaminated specimen should be representativeof the total thickness. The sample is placed between two microscopeslides which are then taped together. The slide is placed on therevolving stage so that the light from lamp 58 shows on the sample. Thebackground lamp 50 is then turned on and the filaments are focused assharply as possible by moving revolving stage 46 up or down, while theyare viewed on the screen. Lamp 50 is then turned off. Stage 46, lamp 58and projection lens 59 are enclosed in a light tight unit. The voltageof power supply 65 is adjusted to give about in. pen deflection and theintensity of the reflected light is recorded on the microampere recorderchart as the sample is rotated through 180.

The heights of the intensity-orientation curve so obtained are measuredin inches from the zero line of the chart at 80 equally spacedorientations and the arithmetic mean of these heights is determined. Tostandardize the randometer characterization, each of the 80 readings ismultiplied by the factor Arithmetic mean to shift the curve to astandard mean (5 in.). The standard deviation of these correctedreadings from this standard mean is then calculated. A perfectly randomsheet would have a standard deviation of zero when the reflected lightis measured at all orientations. As used herein, a random sheet isdefined as one having a standard deviation of 0.6 in. or less, whendetermined by the above-described method. To improve the precision ofthe measurement, several samples selected from throughout the sheet maybe examined and the results averaged. The presence of filament bundlesin the nonwoven sheet can unduly affect the randomness values andtherefore the values lose their significance with sheets having a CVfsabove The following examples are illustrative of the invention.

Example I Using an apparatus assembly essentially as shown in FIGURE 1A,omitting idler roll 3, poly(hexamethylene adipamide) (39 relativeviscosity) is spun through a 34- hole spinneret (each hole 0.009 inch indiameter) into filaments at a rate of 16 grams total polymer per minute,at a temperature of 290 C. The filaments are spun into a quiescentatmosphere at ambient temperature (25 C.) and relative humidity (70%).Downstream (ca. 30 inches) past the point of solidification and about 6inches laterally from the normal filament line, a pneumatic jet (seeFIGURE 3) of the following dimensions is placed:

inlet diameter, inch filament passageway diameter, 7 inch inletcut-downto minimum diameter occurs over filament passageway length, 15/2 inches angle of air entry (below inlet), ca. 15 degrees.

inch The jet, which is grounded, has inlet section or throat 7 composedof aluminum; the body of the jet is composed of brass. The filamentsmake triboelectric contact with the throat of the jet. The receiver is a12 in. x 12 in. aluminum plate which is manually manipulated (hencegrounded). Filaments are collected into hand sheets by interposing thereceiver into the filament line and rotating the same until a sheet ofthe desired thickness and configuration is obtained. The results ofseveral such runs are summarized in Table I.

TABLE I Filament Run A Pressure (P), p.s.1.g.

Denier TIE 1 Mi 2 l Tenacity (T), grams per denier/Elongation (E),percent. 2 Mi equals initial tensile modulus, g.p.d.

In all runs, process operability was very good, uniform sheets with goodfilament separation being produced. Similar sheets are obtained at goodlevels of operability when the polymer used in the above runs ispolycaproamide.

Example II Sheets are prepared from poly(ethylene terephthalate) usingthe apparatus shown in FIGURE 4. Referring to that drawing, filaments lare spun from spinneret 2 and pass in the manner shown over the barguides 20, 21 and 22, thence to the pneumatic jet supplied with airunder pressure through inlet 6. The filament passageway extension 19 isflared outwardly (6) at the terminus 23. The charged filaments 9 whichseparate on exiting the extension of the jet, are collected on analuminum plate receiver 11. The various components downstream from 13spinneret 2 are grounded through leads 12. The pertinent distances alongthe filament line are as follows:

a=17 inches b 19 inches o=22.5 inches 1:25.5 inches e=ca. 4 inches 1: 48inches g=7.5 inches h: 12 inches.

The filaments are quenched with air, applied 6 inches below thespinneret face. The guide bars 20, 21 and 22 are 1 in. x 1 in. withrounded edges and are composed of chromic oxide. Guide bar 21, i.e., thefunctional surface thereof, is offset from the filament line by 2.5 in.Pneumatic jet is shown in greater detail in FIGURE 5. The importantdimensions of the jet are:

inlet diameter, ca. inch filament passageway diameter, 0.05 inch inletangle, 60

angle of air entry, 5

entry 1% inches belowinlet.

The entire jet assembly is fabricated from brass.

In operation, poly(ethylene terephthalate) (34 relative viscosity) isspun through a 30-hole spinneret at a rate of grams (total) polymer perminute. Each spinneret hole is 0.007 inch in diameter. The spinningtemperature, measured at the spinneret, is 287 C. The following resultsare obtained:

TABLE II Filament Properties Air Pressure Run (P), p.s.i.g.

Tenacity, Elong, M1, g.p.d. Denier g.p.d. percent When each of the aboveruns is repeated except that atmospheric steam at about 150 C. isapplied to the separated filaments downstream from the pneumatic jet,using a foraminous member disposed annularly with respect to thefilaments, the filaments relax up to 20% or more with concomitantdevelopment of crimp. Upon later hot calendering, the filaments in thesheet elongate spontaneously, thereby further contributing to the crimplevel in the individual filaments and hence to the properties of thesheet.

When each of the above runs is repeated except that the filaments arecollected in C. water, the filaments again relax, leading to thedevelopment of crimp up to levels of 50 or more crimps per inch (basedon in situ examination). The filaments also spontaneously extend uponsubsequent treatment at elevated temperatures. The filaments also may becaused to relax by employing a heated gas in the pneumatic jet or in arelaxing chamber downstream from the jet.

Examples III-VII In these five examples, nonwoven webs of continuousfilament polyester fibers were prepared under varying conditions ofweb-deposition. Process variables were controlled to give sheets withdifferent degrees of filament bunching, as evidenced by bunchingcoefi'icients ranging from high (0.83) to low (0.57) and CV of 86 to122%. Insofar as possible, other variables were eliminated.

After the webs were prepared, characterization measurements of CVf andbunching coefficient were made. The webs were then bonded by applicationof a copolyester binder solution, and physical properties of the bondedsheets were measured.

Web preparation followed the same general procedure as that described inthe earlier examples, except that corona charging was employed as shownin FIGURE 6. Molten poly(ethylene terephthalate) was spun through a a17-hole spinneret at the rate of 0.88 g./hole/minute into a coronadischarging area, through a jet and thence onto a receiver plate.Spinneret temperature was 288 C., and ambient air temperature was 25 C.The charging area was 72 inches below the spinneretface. The pneumaticjet was substantially the same as that used in the preceding example andwas located 4 inches below the charging area. Air at 60 p.s.i. was used.The tailpipe or exit tube was 18 inches long. The receiver was areciprocating table and was charged opposite to the charge on thefibers. Charging conditions are given in Table III. This table alsoshows results obtained with webs of Examples VIII and IX, made in themanner described below.

CONTINUOUS FILAMENT WEBS V p Web Properties:

Example N o.

a III IV V VI VII VIII IX Web Code A B G D E F G Corona Charge Volts, kv30 28 23 14 i 11 None None Enriching Coefiicient 0.83 0.78 0. 73 0.63 0.57 O. 47 0. 43 CVr. (Percent) 86 90 93 122 121 Filament Properties:

Denier 2. 4 2. 4 2. 4 2. 3 2. 4: 8. 7 .12. 9 Tenacity (g.p.d.) 2.9 2.93.0 2. 9 3. 0 1.2 1.0

longation (percent) 141 i 122 127 117 A 6% binder Tensile strength 3Elongation (percent)- 13 Percent Binder Tensile strength 3 iElongatiou(percent) 1 Webs similar t spectively.

2 Binder applied 3 Lb./in.//oz./yd

0 Examples VIII and IX were found to have CV of and 186%, re-

as a 25% solution in methylene chloride.

Examples VIII and IX The examples immediately above are concerned withnonwoven webs prepared by electropneumatic spinning processes. Thepresent examples concern similar studies on webs made by prior artprocesses.

Web F was deposited by passing a strand of polyester filaments throughan air jet and deflecting the fibers onto a collecting table, employingan angularly disposed deflector plate. No electrostatic charge was givento the fibers. Web G was deposited directly from an air jet onto thecollecting plate without charging Table III shows the characterizationand testing results of the sheets. FIG- URES 11C and 11D are photographsof the webs, G and F, respectively.

After the representative webs were prepared, Ibunching coefiicients weremeasured. The sheets were bonded by the application of a copolymer ofpoly(ethylene terephthalate) and poly(ethylene sebacate) (55/45 moleratio) as binder. The binder was applied by dipping the web into thebinder solution, letting the excess binder drip off, and air drying.Physical properties were then measured using an electronic tensiletesting machine (Instron ieiter). Results of the measurements are givenin Table The results of Table III are, of course, of the highestsignificance. Webs A through C were produced under preferred processconditions. They had CV of below 100% (bunching coeflicients in therange of 0.7 or higher). All of these webs had excellent physicalproperties when bonded.

In addition to the forgoing tests, evaluations were made of the opticaluniformity of the webs before bonding by various techniques. In onemethod the webs were photographed by transmitted light, and alsodensitometer traces of the webs were made. FIGS. 11A and 11B arereproductions of enlarged photographs of webs A and E. FIG- URES A and10B show densitometer traces of the same webs. The tremendousdifferences in appearance of these Webs show that degree of filamentbunching is a significant measure of web uniformity. The densitometertraces serve to emphasize further what is readily apparent to the eye.

The densitometer traces referred to above were obtained using a Leedsand Northrup No. 6700P.I. Recording Microphotometer. The nonwoven webwas mounted between glass plates to constitute the specimen. A recordwas obtained of the light transmission in several transverses across theweb. The figures shown are representative traces replotted to show thelight transmission on a linear rather than on a logarithmic scale.

Another method for evaluation of nonwoven webs for optical uniformityyields numerical values thus permitting a more precise comparison amongvarious webs. In this method, an instrument consisting of a lightsource, sample mount, optical system for focusing the sample image onthe aperture of a photo cell, amplifier and recorder is used to measurethe intensity of light transmitted by the web. Opacity uniformity ismeasured by scanning, at a rate of 6 in./rnin., four 10 in. sides takenfrom a square sample of unbonded web, using a 0.4 in. diameter aperture,which, because of the optics of the system, is equivalent to a 0.1 in.diameter scan area on the web. The uniformity of transmitted lightintensity is characterized by the coefficient of variation intransmitted light' intensity (CV at 50 equally spaced points on therecorder chart for each 10 in. length of sample scanned. The resultsobtained when webs A through E in Table III were evaluated by thismethod are summarized in" Table IV.

The randomness of the unbonded webs A through C in Table III wasdetermined with the optical randometer and the results are given inTable IV.

TABLE IV Randomness Example Web Code Percent Percent Standard CVrB CVtnDeviation A 86 14 0.4 13 90 14 0.4 O 93 15 0.5 D 122 33 E 121 26 Anexcellent correlation is shown to exist between optical uniformity, asmeasured by CV and degree of filament bunching, as measured by CVUniformity of appearance deteriorates rapidly at levels of CV; aboveExample X In this example a series of nonwoven webs is produced whilemaintaining all the operating conditions constant except for the levelof electrostatic charge applied to the filaments. l

The apparatus assembly used in this example is shown schematically inFIGURE 7, wherein the filaments pass directly, as indicated by thedotted lines, from the spinnerets to the target bar of corona dischargedevice 30. Quench chimney 31 and guide roll 3 are not used in thisapparatus embodiment. Poly(ethylene terephthalate) (27 relativeviscosity) is spun through spinneret 2 having 17 holes (0.009 in.diameter x 0.012 in. long) at a total throughput of 18.4 g./ min. whilean 80/20 copolymer of poly(ethylene terephthalate)/poly(ethyleneisophthalate) (29 relative viscosity) is spun through spinneret 2ahaving 20 holes (0.009 in. diameter x 0.012 in. long) at a totalthroughput of 13.0 g./min. The spinneret temperatures are 271 C. and 263C., respectively. Four of the copolyester filaments are used and theother 16 are spun' to waste. The filaments are quenched in the ambientair: at 27 C. before entrance into a draw jet 5 located about 65 inchesbelow the spinnerets. The 21 filaments from the two spinnerets arecombined into a filament bundle at the target bar of corona dischargedevice 30 which is located about 6 inches from the jet inlet.

The corona discharge device consists of a 4-point electrode positionedA; inch from grounded, 1% inch diameter, chrome-plated target barrotating at 10 rpm. A negative voltage is applied to the corona pointsand is varied between 0 and 45 k.v. to vary the level of charge on thefilaments. The filament bundle makes light contact with the target baras it passes between the target bar and electrode. The level of chargeis measured by collecting filaments exiting from the jet in a calibratedpail coulometer and is expressed as c.g.s. electrostatic units (e.s.u.)per square meter of filament surface.

The filaments are drawn and forwarded toward the laydown belt by apneumatic jet 5 having a nozzle section as shown in FIGURE 8 and havingthe following dimensions:

In. Over-all jet length 24 Filament inlet diameter (16) 0.062 Filamentinlet length (16) 0.55 Filament passageway (19) minimum diameter 0.093Metering annulus 32:

Inner diameter 0.0750 Outer diameter 0.0930 Length 0.020

Air at a pressure of 51 p.s.i.g. is supplied to the jet, which underthese conditions applies about 13.5 grams total tension to the filamentbundle. Attached to the bottom of the jet is a relaxing chamber (9 /2in. long; Vs in. inside diameter) which is provided with an annularnozzle for supplying additional air to the relaxing chamber. In this 1 7example, hot air is not supplied to effect heat-relaxation of thefilaments, but room temperature air is added at 4.8 s.c.f.m. to maintainnonturbulent flow in the relaxing chamber.

The jet-relaxing chamber unit is positioned at an angle of 82 with theplane of laydown belt 11 and is moved by traversing mechanism 33 so thatit generated a portion of the surface of a cone, while the output fromthe relaxing chamber forms an are on the laydown belt having a chordlength of 36 inches. The traverse speed is 30 passes (15 cycles) perminute. The distance from the exit of the relaxing chamber to thelaydown belt is approximately 30 inches. The laydown belt moves at aspeed of 12.5 inches per minute. Plate 34 located beneath the belt ischarged at +35 kv., to pin the filaments to the laydown belt. Theproperties of the homopolymer fibers are: denier 2.5 dLp.f. (0.3 tex.);tenacity 3. 2 g.p.d.; percent shrinkage (when heated at water at 70 C.with no restraint), 35.9.

The random nonwoven web so prepared is consolidated by passing between aheated roll (80 C.) and an unheated roll under light pressure. Samplesof the consolidated but unbonded webs are retained for measurement of CVand 0v, and other samples (8 in. x 8 in.)

of the consolidated web are bonded individually 'by heating them in alaboratory press at 220 C., 5,000 lbs. total pressure, for secondsbetween two polytetratluoroethylene-coated grooved plates. The plateshave 24 grooves per inch and are placed with the grooves at right anglesto each other. The total pressure area between the land areas of the twoplates is 4%.

The tensile strengths and formation values of the bonded sheets aredetermined. Formation'value, designated FV, an alternative to CV vforexpressing degree ofuniformity of the nonwoven sheets, is measured witha Paper Formation Tester (M. N. Davis et a1, Technical Association ofthe Pulp and Paper lndustry, Technical Papers, Series 18, 386-391(1935)). Asa standard for determination of FV, a suitable number ofsheets of 1' oz./yd. onion-skin paper are combined to give a basisweight within 0.5 oz./yd.? of the samples to be examined.-

Table V summarizes the charging condition, levels of change obtained onthe filaments and properties of the unbonded webs and bonded sheets.

lished by the tensile strength data. Wide fluctuation in uniformity andunsatisfactory product appearance are obtained with webs having a OVgreater than 100%.

- Data on randomness of the vention meet the webs.

previously defined limit for random Example XI The data in Example X,and also in preceding Examples 111 through VH, were obtained on websprepared with filaments which shrink during the bonding step. Forcomparison a series of webs is prepared with spontaneously elongatablepoly(ethylene terephthalate) filaments and cospun binder filaments of an80/ 20 copolymer of poly(eth- TABLE VI Sample Percent CV TensileStrength lb./in.//oz./yd.

These data confirm the importance of having a high level of uniformfilament separation (CV l00%) to obtain high strength levels with agiven fiber tenacity.

Example XII The suitability of nonwoven sheet samples A through K inExample X for use in window-shade cloth is determined by making pinholecounts. These counts are made on 3 l-in. square samples of each sheet.The sheets, which have constant filament cross-section and denier, arechosen to have basis weights of 4.5 $0.25 oz./yd. An image of the TABLEV Electrostatic charge Tensile Randomness, Sample Percent Percent FVStrength, Standard Voltage Charge 011 CV tli lb./in.//oz./ycl. DeviationApplied Filaments (in.)

(kv.) (esu/mfl) FIGURE 12 is a graph of the tensile strength and CV datain Table V. Since these data are for nonwoven webs having the samefilament strengths, the data are highly significant and the graph showsclearly that there is a rapid drop in tensile strength at a OV above100%. The data in Table V also indicate a sign ficant and rapiddeterioration of uniformity of appearance, as measured either by CV orformation value, at values of CVf greater than 100%, the same criticallevel as that establ-in. square sample is projected onto a screen at alinear magnification of 7 with a 35-min. projector. The total number ofpinholes (bright spots of light) is then counted. An alternativeprocedure is to project an image of a l-in. square of sample ontophotographic paper through an enlarger (7 x) to obtain a permanentrecord of the sample. Pinholes lead to blackening of the paper and arecounted directly using a Zeiss particle size counter. The data obtainedare summarized in Table VII.

nonwoven webs .are also int cluded in Table V and indicate that the websof this in-' Below a CV; of 100%, the number of pinholes is relativelysmall and the sheets are useful as shade-cloth materials. Above a CV of100%, the number of pinholes increases three to five-fold and noreasonable amount of masking with opaque coatings will produce a usefulshade cloth.

Example XIII The abrasion resistance of bonded nonwoven sheets fromExample X is determined using the C.S.I.A. abrader. The conditions ofthis test are as follows: 1 in. x 2 in. sample size; abradant, load, 5lb./in.; 2 cycles/minute. The results are summarized in Table VIII.

TABLE III Sample Percent CV Cycles to Minimum Cycles Failure 1 toFailure 1 Average of 8 samples.

The data indicate the poorer abrasion resistance of the nonuniformsheets. The data on minimum cycles to failure are included to point outthat certain areas of the nonuniform sheets fail quickly and result infailure for the entire fabric.

Example XIV Bonded nonwoven sheets of continuous poly(ethyleneterephthalate) filaments, having diflferent degrees of uniformity offilament separation because of bunches of filaments in the structure,are imbedded in rubber and then evaluated in the standard air-wick testfor acceptability as chafer materials in tubeless tires. The samples forevaluation are prepared by imbedding 1 in. x 3 in. pieces of fabric inrubber by a molding operation. The molded test sample is formed so thatfabric ends extend. from two edges of the sample. The sample is thenmounted in a pressure apparatus which exposes one edge of the sample topressure. Leaks are detected by coating the other edge with a detergentsolution and looking for air bubbles. Three samples from each nonwovensheet are tested with the following results:

Sheet Percent CF18 Results No failures at 100 p.s.i. One failure after30 min. at 100 p.s.i. One failure after min. at 100 p.s.i.

Example XV for tenting materials by coating with 68% by weight of Zincoxide 5 Rutile titanium dioxide 10 Phthalocyanine green pigment 3 Thecoating is applied from a xylene medium at 20% solids. The coated sheetsare evaluated for water repellency by a rain-impact test as follows: Thesample (6" x 12 or larger) to be tested is placed over a funnel (5" x5") shaped like a roofless house and having a ridge pole connectingsymmetrically located apexes on 2 opposing sides. The apexes are 1% in.higher than the top edges of the other 2 sides. The sample is held inplace by 2 clamps (weight 4 lbs. each) attached to the narrow ends ofthe sample. In order to prevent wicking of water /2 in.-widevapor-impermeable tape is placed on the sample where it contacts theridge pole and the edge of the funnel. Water is allowed to fall as dropson the mounted sample from a 5" x 5" tray positioned 60 in. above thesample. The tray has holes positioned in a rectangular arrangement onabout /2 in. centers. The total rate of flow of the water is 1.5 gal.per min. The water leaking through the sample into the funnel in 30minutes is measured. The results are summarized below:

These data indicate the desirability of having uniform filamentseparation (CV Higher coating weights are required to obtain acceptablewaterproofing when nonuniform sheets are used.

Example X V1 The apparatus of Example 11 is employed in the preparationof sheets composed of polypropylene filaments. The pertinent distancesare the same except for the following (see FIGURE 4):

a=18 inches 11:22 inches c=30 inches d=38 inches Guide bar 21 is offsetfrom the filament line by 2 in. Polypropylene (10 melt-index) is spun ata rate of 6 grams per minute through a 30-hole spinneret, each holebeing 0.009 inch in diameter. The temperature at the spinneret is C.Uniform sheets are obtained. Using 19 p.s.i.g. air, the followingproperties are obtained in the individual filaments, as spun: tenacity,2.35 g.p.d.; elongation, 369%; modulus, 17.9 g.p.d.; denier, 1.51.

Example XVII Following the general teaching of Example XVI, sheets wereprepared of continuous filament, predominantly isotactic polypropylene.Triboelectric charging was accomplished with 3 brass bars. Spinningconditions were adjusted to obtain high-tenacity filaments. A 30-holespinneret with holes 0.015 inch in diameter was used to spin polymerhaving a melt index of 12.4. A two-stage mechanical drawing process wasused. Other spinning variables are shown in Table IX below. After thewebs were deposited, they were bonded by the application of 21- 24% byweight of polyvinyl chloride in tetrahydrofuran solution. Fiber andfabric properties for two samples made as indicated are shown in TableIX.

TABLE IX Fiber Properties Fabric Properties Polymer Draw TensileStrength Web throughput Ratio (g./hole/min.)

Den T (g.p.d.) E. (percent) Mi lb./in./oz./yd. E. (percent) XVII-1 0.15.5x 1. 09 4. 9 72 25 21 46 XVII-2 0. 16 10.5X 1. 65 7. 8 26 47 33 26Example XVIII The following example illustrates co-spinn-ing of poly-(rhexamethylene adipamide) (39 relative viscosity) and a 10% (weight)polycaproamide copolymer (relative viscosity 45) thereof. The 66-nylonis spun from a 34- hole spinneret (0.009 inch hole diameter) at 16 totalgrams per minute at 290 C. The 66/6-nylon copolymer is spun from a20-hole spinneret (0.009 inch hole) at 255 C. and the output from 2holes (1.78 grams per minute) is combined with the 34 filaments of66-nylon. The two spinnerets are located on 5.5 inch centers. Thefreshly spun filaments are passed over a grounded, polished aluminum barlocated 40 inches below, parallel to and offset by 6 inches from thecenterline of the spinnerets. A pneumatic jet as shown in FIGURE 3 islocated 1 inch below the point where the filaments contact the bar. Airat p.s.i.g. is supplied to the jet. The receiver, a 42 in. x 42 in.grounded aluminum plate, is located inches below the pneumatic jet. Thereceiver is traversed at a speed of 280 inches per minute below the jetand is further traversed at a speed of 28 inches per minute in adirection perpendicular to the primary traverse. Collecting in thismanner for about 8.5 minutes yields a uniform sheet having a 4-ounce persquare yard basis weight. The spinning speed during this run, based onpolymer throughput and final filament denier, is 2900 yards per minute.Typical properties of 6'6-nylon filaments prepared by this procedureare: 'T/E=3.5/ 165; Mi=7.5; denier per filament, 1.60.

During the process described, the filaments are chargedtriboelectrically as they pass the aluminum bar; they are orientedupstream of the pneumatic jet, partly at the bar and partly by aspin-draw mechanism upstream from the bar. By virtue of the co-spunbinder fiber, the resultant sheet can be rendered more stable byheating. For example, the sheet is pressed between SO-mesh stainlesssteel screens at 50 p.s.i. at 200 C. for 1 minute, to yield a tough,drapable fabric which exhibits enhanced resistance to delamination. Atypical fabric prepared by this method has a tensile strength of 10lbs./in./oz./yd.

Using an apparatus assembly similar to that described in Example II,poly(ethylene terephthalate) is spun through a 68-hole spinneret while a20% (weight) poly- (ethylene isophthalate/terephthalate) copolymer iscospun through an adjacent 34-hole spinneret, incorporating at least twoof the latter filaments in the resulting sheet. A uniform sheet isobtained which, by virtue of the cospun binder fiber). can be renderedmore stable by subsequent heating. Taking in consideration the differentcompositions, the instant sheets are comparable to the ones obtainedhereinabove as regards uniformity of laydown, freedom from filamentaggregates, and the like; enhanced stability after heating,characteristic of sheets prepared by co-spinning, also is observed.

Example XIX The bundle of filaments is quenched in the ambient airbefore entrance to a draw jet, located about 70 in. below the spinneret.An operating pressure of 40 p.s.i. in the draw jet would provide atension of about 3 grams on the threadline, as measured immediatelyabove the jet. A negative corona is formed from a four point source 8in. above the entrance to the draw jet, and above A in. from the bundleof filaments. A rotating target bar (10 r.p.m., 1% in. diam.) makes aslight contact with the filaments and aids in maintaining a uniformdistance between individual filaments and the corona source. A negativevoltage of 30-40 kv. (200-250 ,ua.) is applied to the corona points.

The charged poly(ethylene terephthalate) filaments are deposited on areciprocating table (30 in. square) charged to positive polarity (20kv.). The speed of the table movement is adjusted to obtain the properbasis weight and satisfactory uniformity. Under the table speedconditions of 29 in./min. in one direction and 580 in./min. in the otherdirection, the charged fiber is deposited as a web at a rate of 0.8oz./yd. per minute. The filament properties are:

Denier d.p.f 2.3 Tenacity g.p.d 2.9 Elongation 183 Mi g.p.d 172 ExampleXX This example illustrates the production of a typical elastomericpolypropylene web. Polypropylene flake (Profax) at an MI of 10 is screwmelted at a. maximum temperature of 290 C. andmetered at a. 12 g./min.rate through a A in. layer sand filter bed and a 2 in. spinneret having20 capillaries (0.015 in. diaml x 0.020 in. long). The packblock is heldat 275 C. and the spinneret ternperature is controlled at 260 C. I

The bundle of fibers is quenched radially in a 6 in. long quench chimneyusing 40 c.f.m. air at room temperature. The top of the quench chimneybutts against the bottom of the spinning pack to minimize the effect ofair flow on the spinneret temperature.

A draw jet operating at 25 p.s.i. provides a tension of about 3 grams onthe threadline, measured immediately above the jet. Distance fromspinneret to jet entry is 72 in. A negative corona is formed from a fourpoint source at a distance of A; in. from a 1 /4 in. OD. bar rotating at10 r.p.m. The threadline makes light contact with the target bar, thecenterline of which is 8 in. above the entrance to the draw jet. Anegative voltage of 20-25 k.v. (-150,:ra.) is applied to the coronapoints.

The elastomeric, charged fibers are deposited on a grounded 47 in.square table which reciprocates in two directions to form a web. Tablemotion is adjusted to obtain proper web weight and satisfactory webuniformity. Several layers are made for each. sheet. For the conditions23 above, table speed is 26 in./min. in one direction and 570 in./min.in the other direction, and each layer is 0.5 oz./yd.

Typical fiber properties are as follows:

Denier d.p.f 2.5 Tenacity g.p.d 2.0 Elongation percent 300 Mi g.p.d.. 14

The web formed in this manner is coherent and strong, even withoutbonding. The appearance of the web is uniform. The bunching coefiicientof the web is 0.75.

Example XXI The non-woven Webs of this invention, described in examplesabove, were found to offer advantages as bases for water-proofedmaterials. Several samples of such fabrics were waterproofed with waxes,wax-resin combinations and resins. In comparison with similar fabricsprepared from woven cotton base material, the novel coated fabrics werefound to retain their water-repellency much longer when subjected toscrubbing and flexing action.

The experimental fabrics were similar to those described in Example XIX,except that several different basis weights were used. Wax coatings wereapplied using commercial wax-solutions and wax-vinyl resin solutionsemployed as water-proofing compounds. Commerciallycoated fabrics werepurchased and tested for comparison purposes. Resin coatings employedincluded both vinyl and chloro-sulfonated polyethylene resins.

Table X lists several experimental and control materials, which wereprepared or purchased as indicated. Samples of such material weresubmitted to the indicated number of scrub/flex cycles using amechanical flexor and were then tested using an AATCC HydrostaticPressure Tester.

As the table shows, improvements over comparable cotton fabrics rangedfrom 30:1 to 300: 1.

The laminated structure, due to the continuous nature of the reinforcingfiber elements, was observed to have greater strength and impactproperties than similar staplereinforced materials. The structure washeat-scalable with no loss in properties at the seal.

Example XXIII Other laminated combinations are possible using thenonwoven webs of the present invention as well. A web of the type shownin Example XX, but containing highly oriented polypropylene material incontinuous filament form, was laminated to a self-supporting film oforiented poly-propylene. First the fiber web was deposited, consolidatedand thermally self-bonded. The oriented polypropylene film, of the typeknown in the art, was coated with a low-melting polyethylene adhesive.Then the two components were laminated with the application of heat andpressure to activate the adhesive. The result was a high level oflamination of web to film with a moderate level of fiber-to-fiberbonding. The resulting structure was highly suited to use as an improvedindustrial film suitable for protective coverings. Equally well, thestructure was suited for use as a material for shipping bags. Thepresence of the film gave a vapor-impermeable barrier while the fiberelements provided high tear resistance and tensile strength.

In a modification of the practice of this example, a portion of the sameself-bonded web was melt-coated with an unoriented film of polypropyleneapplied to one side.

Example XXIV This example shows the preparation of nonwoven webs ofpolypropylene and the lamination of such webs to give a highly resilientsemi-rigid sheet structure.

Stereo-regular polypropylene having a Melt Index of 12.4 was spun into aweb following the general procedure of Examples III through VII. In thepresent example the TABLE X.SCRUB/FLEX RESISTANCE OF WATERPROOFING ONCOTTON AND ON CONTINUOUS FILA- MENT NONWOVEN FABRICS WaterproofingHydrostatic Pressure, Cm. Gray Scrub Repelleney Item Fabric Weight,Flex, Retained,

oz./yd. Cycles Before After percent Compound Operation Scrub] Semb/ FlexFlex Woven Cotton Commercial 10 78 13 16. 7 d do 10 68 14 20.6 d0 10 10025 25.0 Laboratory 3, 000 48 23 48. 0 do 10 51 13 26.0 100 10 38. 0 10035 18 52. 0 3, 000 48 26 55. 0 3, 000 31 20 64. 5 3, 000 22. 5 18 80. 020 54 17 31. 5 20 67 18 26. 9 1, 200 43 24. 5 57. 0 1, 300 25 17.5 70. 05 26. 5 14. 5 57. 0 5 29. 0 l5. 5 53. 5 150 28 10 35. 8

1 Continuous filament nonwoven. Chlorosulfonated polyethylene.

Example XXII Continuous filament nonwoven sheets were prepared accordingto the teachings of Example 11. Webs having a basis weight of 1.0 and2.0 oz./yd. were prepared. The filaments were all of poly(ethyleneterephthalate) and no bonding filaments were included.

After sheet formation, the web structures were individually laminatedwith polyethylene films by a simple hot pressing procedure. Atemperature of 195 C. was used to effect bonding, and a pressure of 125p.s.i. was employed. The nonwoven web was imbedded in the thermoplasticfilm which thus acted as a binder for the web.

tray having an area of 2 sq. ft. The web density was 2 oz./yd. A numberof Webs were collected in this way and each web was consolidated bypressing between plates at 115 C. at a pressure of tons/ft. for 30seconds.

26 as follows: isotactic polypropylene (melt flow rate MFR 12, by methodof ASTM1238 at 230 C. with a loading of 2.16 kg.) is spun from each oftwo spinnerets. One spinneret has 30 spinning orifices each 0.015 in. indiam- Six of the consolidated webs were plied together to 5 eter whilethe other has 5 orifices each 0.015 in. in digive a composite laminateweighing 12 oz./yd. The comameter. The extrusion rate from the latter is3 g./min. posite web was needle punched on a needle loom at a whilepolymer is extruded from the 30-hole spinneret at density of 740needles/fe the machine being run at 85 18 g./min. The temperature of the30-hole spinneret is strokes/min. The web was run through the loom at a256 C. and that of the 5-hole spinneret, 221 C. speed of 14 ft./second.The filaments from the 30-hole spinneret are led to Following the samegeneral procedure described above, a heated feed roll operating with asurface temperature a number of these laminated resilient structures ismade of 118 C., and advanced by means of an idler roll in varying basisweights. The resulting fabrics are canted with respect to the heatedroll. A total of 5 wraps described in Table XI. The resilience andindentation is used on the heated feed roll, which is operated withresistance of the sheets are given as well. a surface speed of 238yd./rnin. From the heated feed Because of their excellent response tophysical deformaroll the filaments are then passed 5 wraps around antion, these sheets olfer advantages for use as floor tiles, idlerroll/draw roll system operating cold with a surface stair-stepcoverings, rug underlay material, counter-top speed of 842 yd./min.These filaments are drawn 3.54 coverings, resilient game-table surfaces,and similar appliare 7.75 denier (0.86 tex.) per filament and have acations. In particular, the high resistance to permanent tenacity of3.76 g.p.d. indentation and the superior resilience indicate excellentThe filaments issuing from the 5-hole spinneret are behavior as floortiling materials. I led to a heated roll operating with a surfacetemperature TABLE XI Indentation Resistance (mils residual set) QThickness Basis Thickness, Resilience After 10 Weight, mils 200 6003,000 Thousand onlyd. p.s.i., p.s.i., p.s.i., Impacts of 24 hr. 1hr.1hr. Percent Percent lit-lb.

Compres- Work sion Recovery Example XXV of 95 C. and a surface speed of667 yd./min. After being in contact wtih the heated roll for 180 thefila- A web of poly(ethylene terephthalate) fibers and co- I tion escrie in t e secon par 0 xamp e Spinning conditions were the same as thosedescribed in 3:; 22 25221 gg fg g 22 2 3 it igg ig ig Example XIX,except that the binder fibers were added filaments am 7 8 nieg 86 teX erfilament and have to the bundle of polyester filaments upstream of the t55 p t f I th t 0 Charging Stage. 45 a enaci y o g.p. e amen s mm c wDownstream of the drawing jet, the filaments were relaxed and shnmk in acontinuous manner by running them through a chamber containingcocurrent-fiowing air at 550 C. The walls of the chamber were maintainedat room temperature. The air-flow of the hot air was not greatly fasterthan the entering velocity of the filaments into the relaxing chamber,but substantially faster than the exit velocity of the filaments. Duringtheir exposure to the hot air, the filaments shrank continuously in thechamber, losing 25% or more of their original length by relaxation. Thisrelaxation placed the polyester filaments in a state of spontaneouselongatability as already described. Following the relaxation-shrinkagestep, the filaments were collected as described in Example XIX to obtaina uniform nonwoven sheet of polyester fibers and co-spun binder fibers.

The web was then placed between a -mesh wire screen on one side, and acanvas fabric on the other, and heated to 210 C. at 200 p.s.i. for oneminute. The heating caused elongation of the polyester fibers withbonding and embossing taking place simultaneously. The fabric producedas described was a soft, flexible nonwoven textile-like material,suitable for the same uses as woven fabrics of similar basis weight. Thehighly crimped fibers rendered the final structure drapable, and gave ita pleasing handle.

Example XXVI A nonwoven web of 14% low-oriented and 86% highorientedcrystalline polypropylene filaments is prepared splnnerets meet and areguided so that the low-oriented filaments are dispersed uniformlythroughout the highoriented filaments.

The filaments are stripped from the draw rolls and forwarded by apneumatic jet having a nozzle section as shown schematically in FIGURE 8and having the following dimensions:

Inc-hes Over-all jet length 15 A Filament inlet diameter (16) 0.062

Filament inlet length (16) 0.55

Filament passageway (19) minimum diameter 0.093 Metering annulus (32)Inner diameter 0.0750

Outer diameter 0.0930

Length 0.020

The jet is supplied with air at p.s.i.g. and applies a tension of about36 grams on the filament bundle. The entrance to the jet is 110 inchesfrom the draw roll.

Between the draw roll and the jet and 7 /2 inches from the latter, thefilament bundle is exposed to a corona discharge device to impart anelectrostatic charge to the fibers. The corona discharge device consistsof a 4-point electrode positioned inch from a grounded, 1% inchdiameter, chrome-plated target bar rotating at 10 rpm. A negativevoltage of 23 kv. microamperes) is applied to the corona points. Thefilament bundle passes between the target bar and electrode and makeslight contact with the target bar and is charged to a value of 74,100

75 6.S.H./LI11.2 of filament surface.

1. A SUBSTANTIALLY UNIFORMLY OPAQUE NONWOVEN SHEET OF NONPARALLELCONTINUOUS SYNTHETIC ORGANIC FILAMENTS, THE CONTINUOUS FILAMENTS BEINGRANDOMLY DISTRIBUTED THROUGHOUT SAID SHEET AND SO DISPOSED AS TO BESUBSTANTIALLY SEPARATE AND INDEPENDENT OF EACH OTHER EXCEPT AT FILAMENTCROSS-OVER POINTS WITHIN THE SHEET, THE FILAMENT SEPARATION DISTANCESHAVING A COEFFICIENT OF VARIATION, CVFS, OF NO GREATER THAN ABOUT 100%.